There are 3913 changes that have been made to the Book of Mormon, some of which are significant doctrinal changes.
Many Mormon church members, including church leaders, stumbled across the changes them selves, and noticed the doctrinal significance. Here is a video of just one such faithful member (a bishop), who was following the LDS prophets council to read the Book of Mormon, when he came across changes and facts that he couldn’t ignore:
These combined with Joseph Smith’s changes to the “first vision”, have lit sparks that have caused many Mormons to leave the LDS church.
The LDS church has come out with apologetics on the topic, but only address small changes and completely ignore the significant doctrinal changes.
For more information on the subject you can read: